1. Field of the Invention
The present invention relates to a roller and cage assembly, and more particularly, to a roller and cage assembly having a favorable lubrication property and which is suitable for high-speed rotation.
2. Description of the Prior Art
Roller and cage assemblies that take advantage of the characteristics of having a small cross-sectional height and large load capacity were frequently used in the past for the connecting rods of motorcycle engines.
FIG. 1 shows a roller and cage assembly of the prior art. This roller and cage assembly is disclosed in Japanese Utility Model Laid-Open Publication No. 4-41115.
As shown in the drawing, this roller and cage assembly is composed of cage 1, in which a plurality of roughly cylindrically shaped pockets 1a are formed at equal intervals and parallel to the axial direction, and rollers 2, which are inserted into each of said pockets 1a.
Cage 1 forms two rings 1b, and bars 1c, which mutually couple both said rings 1b and demarcate said pockets 1a together with each of said rings 1b, into a single unit. One pair each of inner retaining projections 1g and outer retaining projections 1h are formed on both of the insides as well as on both of the outsides of both ends of these columns 1c. These inner retaining projections 1g and outer retaining projections 1h project so as to face pockets 1a, and as a result, rollers 2 are restricted from falling out of pockets 1a.
The above-mentioned inner retaining projections 1g and outer retaining projections 1h are formed by providing two each of caulking grooves 1i and 1j in both the inner and outer surfaces of bars 1c so as to extend in the circumferential direction. These caulking grooves 1i and 1j act as oil grooves resulting in efficient lubrication.
Recently, the rotating speeds of engines have tended to increase. In order to allow the roller and cage assembly of the prior art to be compatible with these increasing engine speeds, the lubricating property was improved by providing oil grooves like those described above to prevent wear and seizure. However, the rotating speeds at which the roller and cage assembly of the prior art was able to withstand were still not satisfactory. Thus, this is a problem that should be solved in terms of development of engines having even higher rotating speeds.
Furthermore, although the lubrication property increases if the number of concave portions acting as oil grooves is increased or their area is expanded, since the rigidity of the cage decreases proportionally thus preventing it from being used practically, this cannot be performed simply.
On the other hand, in the roller and cage assembly of the prior art, wear and seizure is suppressed by performing copper or silver plating in order to accommodate increasing engine speeds. Although roller and cage assemblies on which silver plating has been performed allow the obtaining of favorable high-speed rotation performance in comparison with those on which copper plating has been performed, the maximum rotating speed these roller and cage assemblies are able to withstand is roughly 13,000 rpm. When the rotating speed is increased beyond this point, the disadvantage results in which wear and seizure occur even if considerably large amounts of lubricating oil is supplied. In addition, plating treatment using silver results in high costs, and this is also a problem that should be solved in terms of engine development.
Moreover, the roller and cage assembly of the prior art generates remarkably high levels of heat during high-speed rotation. In addition, it is also considerably heavy. These are also problems that should be solved in terms of engine development.